Rev 1; 1/09
Cache-Memory Battery-Backup Management IC
General Description
The DS2731 is a complete power-management solution
for modular backup applications. It is well-suited for 2.5V
and below memory bus voltages, with an input voltage of
12V. The DS2731 includes an internal MOSFET switching
power stage for charging a one-cell lithium chemistry bat-
tery. It has a fully integrated synchronous buck regulator
capable of supplying up to 450mA of cache backup sup-
ply current, and the necessary logic and power devices
for handling the switchover from system power to battery
power. The battery charging method of the DS2731 is
constant current/constant voltage (CCCV). Output voltage
can be margined from 3.8V to 4.6V using a resistor-
divider. Charge is terminated when the charging current
falls below 5% of full charge current. Switchover to battery
backup is initiated by an internal comparator and occurs
automatically when a sensed-input voltage drops below
2.93V. At light loads, the 2MHz internal synchronous buck
regulator operates in burst mode for maximum efficiency.
All nonessential functions of the DS2731 are disabled
while supplying holdup current to the cache memory, and
the IC goes into very low-current dormant mode when the
battery voltage drops below a user-settable threshold.
The DS2731 keeps track of charge status and signals the
user through open-drain I/O pins that can be used to
drive LEDs.
o
Lithium Chemistry CCCV Charger
o
Adjustable Regulated Charging Up to 1.5A DC
o
Adjustable Charge Voltage from 3.8V to 4.6V
o
External and Internal Thermal Protection
o
Safety Timer Secondary Termination
o
LED Indicator Outputs
o
Detects Power Outage and Switches Between
Normal Power and Backup Battery
o
Adjustable High-Efficiency Synchronous Buck
Regulator with Skip Mode at Light Loads
o
Low-Power Consumption in Discharge Mode
Features
DS2731
Ordering Information
PART
DS2731E+
TEMP RANGE
-20°C to +70°C
PIN-
PACKAGE
28 TSSOP-EP*
(173 mils)
28 TSSOP-EP*
(173 mils)
TOP
MARK
DS2731
DS2731
DS2731E+T&R -20°C to +70°C
Applications
RAID Controller Card
+Denotes
a lead(Pb)-free/RoHS-compliant package.
T&R = Tape and reel.
*EP
= Exposed pad.
Typical Operating Circuit
TOP VIEW
+
MARGIN
STMR
1
2
3
4
5
6
7
8
9
10
11
12
13
14
*EP
Pin Configuration
28
27
26
25
24
23
22
THM
RSET
BATT+
SNS
CGATE
VIN
CHG1
CHG2
CGND1
CGND2
CHARGE
FAULT
DONE
ENC
DS2731
MAIN
POWER
SWITCH MODE
CHARGER
(CCCV)
CTG
AUX
CBIAS
LITHIUM
BACKUP
CELL
VREG
CIN
LX
SGND
AGND
REF
LO_BATT
DS2731
21
20
19
18
17
16
15
AUXILIARY
POWER
POWER
MANAGEMENT
SWITCHING
REGULATOR
CACHE
MEMORY
DIV
ENS
TSSOP
*EXPOSED PAD
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Cache-Memory Battery-Backup Management IC
DS2731
ABSOLUTE MAXIMUM RATINGS
Voltage Range on CGND1, CGND2, and
SGND Pins Relative to AGND ...........................-0.3V to +0.3V
Voltage Range on VIN, CHG1, CHG2, and
CGATE Pins Relative to AGND........................-0.3V to +16.0V
Voltage Range on CHARGE, FAULT, and
DONE Pins Relative to AGND .........................-0.3V to +16.0V
Voltage Range on Any Other Pin Relative
to AGND ............................................................-0.3V to +6.0V
Continuous Sink Current on VIN, CGND1,
CGND2, SGND, AUX, BATT+ Pins ......................750mA each
Continuous Source Current on CHG1,
CHG2, and LX Pins ..............................................750mA each
Continuous Sink Current on CHARGE,
FAULT, and DONE Pins .........................................20mA each
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-55°C to +125°C
Soldering Temperature...........................Refer to the IPC/JEDEC
J-STD-020 Specification.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED OPERATING CONDITIONS
(V
IN
= +10.8V to +13.2V, T
A
= -20°C to +70°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Charger Supply Voltage
Auxiliary Supply Voltage
Battery Voltage
LED Voltage
(CHARGE, FAULT, DONE Pins)
Charger Enable (ENC)
Switcher Enable (ENS)
SYMBOL
V
IN
V
AUX
V
BATT+
(Note 1)
(Note 1)
Operating as input (Note 1)
(Note 1)
(Notes 1, 2)
(Notes 1, 2)
CONDITIONS
MIN
10.8
3.0
2.7
0
0
0
TYP
12.0
MAX
13.2
3.6
5.0
V
IN
+ 0.3
V
CBIAS
+ 0.3
V
CIN
+ 0.3
UNITS
V
V
V
V
V
V
CHARGER CIRCUIT ELECTRICAL CHARACTERISTICS
(V
IN
= +10.8V to +13.2V, T
A
= -20°C to +70°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Charger Idle Supply Current
SYMBOL
I
IN
I
AUX
Regulator Supply Current
(Note 3)
I
BATT+
I
SLEEP
C
BIAS
Regulator Voltage
C
GATE
Regulator Voltage
C
GATE
Capacitance
C
BIAS
Capacitance
Enable Logic-Low (ENS, ENC)
Enable Logic-High (ENS, ENC)
V
CBIAS
V
CGATE
C
CGATE
C
CBIAS
V
IL
V
IH
(Notes 4, 5)
(Notes 5, 6)
1.6
2.2
0.22
0.4
CONDITIONS
V
IN
> V
UVLO-CHG
(Note 3),
V
AUX
= 3.3V
V
AUX
> V
TRIP
V
AUX
< V
TRIP
,
V
BATT+
> V
SLEEP
,
ENS
disabled
V
IN
= V
AUX
= 0.0V,
V
BATT+
< V
SLEEP
3.3
V
IN
- 4.0
MIN
TYP
1
100
100
150
10
MAX
UNITS
mA
µA
µA
µA
V
V
µF
µF
V
V
2
_______________________________________________________________________________________
Cache-Memory Battery-Backup Management IC
CHARGER CIRCUIT ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= +10.8V to +13.2V, T
A
= -20°C to +70°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Enable Hysteresis (ENS, ENC)
Pulldown Resistance (ENS, ENC)
LED Outputs Low
(CHARGE, DONE, FAULT)
Fault LED Flash Rate
Preconditioning Charge
Threshold
Preconditioning Hysteresis
Preconditioning Charge Current
Precondition Timeout
Charge-Current Range
(RSET Resistance)
Charge-Current Accuracy
Overcurrent Clamp
Constant-Voltage Threshold
Range
MARGIN Pin Leakage
Constant-Voltage Charge
Accuracy
Charge Termination (CV) Current
Charge-Restart Threshold
Safety Timeout Range
(STMR Resistance)
Safety Timeout Error
SYMBOL
V
HYS-EN
R
PD
V
OL
f
FAULT
V
MIN
V
HYS
I
PRE
t
PRE
I
CHG
I
ERR-CHG
Charge current determined by RSET
(Note 7)
RSET resistor tolerance 0.1%,
R
SNS
= 0.050
Charge voltage determined by MARGIN
pin voltage
V
BATT+
< V
MIN
(Note 1)
2.55
50
5.0
27
0.5
5.0
-5
1.7
3.6
-2
-25.0
4.0
94
1
22
-5
0.83
8
I
CHG
= 1A, V
IN
= 10.8V
(Note 10)
I
CHG
= 1A, V
IN
= 10.8V (Note 10)
V
IN
= 0V, V
CV
= 4.2V, ENC = 0V
V
IN
= 12V, V
CV
= 4.2V, ENC = 0V
No charge current, V
IN
= 12V
Using typical application components
-2
1
1.00
10
0.4
0.15
10
10
+2
µA
µA
µA
ms
5.0
95
4.2
I
OL
= 10mA
4
2.60
100
10.0
30
15.0
33
1.5
1.6
+5
2.5
4.6
+2
+25.0
6.0
96
10
220
+5
2.70
CONDITIONS
MIN
35
100
TYP
70
200
MAX
140
300
1.0
UNITS
mV
k
V
Hz
V
mV
% of
I
CHG
min
A
k
%
A
V
µA
mV
% of
I
CHG
% of
V
CV
hr
k
%
µs
V
DS2731
I
OVERCURRENT
RSET = 0 or R
SNS
= 0
V
CV
I
LEAKAGE
V
ERR-CV
I
TERMINATE
In constant-voltage mode
V
DELTA
t
SAFETY
(Note 8)
t
ERR-SAFETY
R
STMR
= 22,000
Battery Charger Switching Period
t
SW-CHG
Full load (1.5A) (Note 9)
Charger Undervoltage Lockout
High-Side MOSFET
On
-
Resistance
V
UVLO-CHG
R
DSON-CP
Low-Side MOSFET On-Resistance R
DSON-CN
Reverse Leakage of Charge FET
(CHG1, CHG2)
Forward Leakage of Charge FET
(CHG1, CHG2)
SNS Leakage Current
Startup Time
I
REVERSE
I
FORWARD
I
LKG-CHG
t
START
_______________________________________________________________________________________
3
Cache-Memory Battery-Backup Management IC
DS2731
BUCK REGULATOR AND POWER MUX CIRCUIT ELECTRICAL CHARACTERISTICS
(V
IN
= +10.8V to +13.2V, T
A
= -20°C to +70°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Auxiliary Input Trip Threshold
Auxiliary Input Trip Hysteresis
Multiplexer Delay
Break-Before-Make
Power Multiplexer On-Resistance
Regulator Output Voltage Range
DIV Pin Voltage Range
Regulator Output Voltage Error
Low-Battery Threshold
Adjustment Range
LO_BATT Pin Voltage Range
V
REF
Voltage
V
REF
Load Range
(Equivalent Resistance)
Buck Regulator Switching Period
Regulator Undervoltage Lockout
Switching Power
pFET Resistance
Switching Power
nFET Resistance
nFET Off Threshold
Switching Power
pFET Overcurrent Limit
Switching Power
nFET Overcurrent Limit
VREG Pin Leakage
SYMBOL
V
TRIP
V
HYS-TRIP
t
BREAK
R
MUX
V
REG
V
DIV
V
ERR-REG
V
SLEEP
V
LO-BATT
V
REF
I
REF
t
SW-REG
V
UVLO-REG
R
DSON-SP
R
DSON-SN
I
OFFN
I
OCLP
I
OCLN
I
LKG-REG
I
OUT
= 100mADC
BATT+ = 3.0V, V
AUX
= 0 (Note 10)
I
OUT
= 100mADC
BATT+ = 3.0V, V
AUX
= 0 (Note 10)
0
500
400
-2
40
750
650
50mA (Note 9)
2.45
(Note 9)
(Note 1)
Relative to actual V
TRIP
Switching to/from BATT+
(Note 11)
I
MUX
= 10mA, BATT+ or AUX source
Set by V
DIV
pin voltage
0.9
0.4
-5.0
2.75
0.6
1.220
1.22
1000
500
2.70
0.6
1.2
80
1000
900
+2
mA
mA
mA
µA
1.238
0.6
CONDITIONS
MIN
2.85
50
TYP
2.93
80
MAX
3.00
150
1
1.0
2.5
V
REF
+5.0
3.00
V
REF
1.260
126.00
10
V
V
%
V
V
V
µA
k
ns
V
UNITS
V
mV
µs
4
_______________________________________________________________________________________
Cache-Memory Battery-Backup Management IC
THERMAL PROTECTION CHARACTERISTICS
(V
IN
= +10.8V to +13.2V, T
A
= -20°C to +70°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
THM Pin Internal Pullup Voltage
THM Pin Internal Resistance
Thermistor Overtemperature
HALT Threshold
Thermistor Overtemperature
Resume Threshold
Thermistor Undertemperature
HALT Threshold
Thermistor Undertemperature
Resume Threshold
Thermistor Disable
Threshold
Internal Overtemperature
Protection Threshold CCCV
Internal Overtemperature
Hysteresis CCCV
Internal Overtemperature
Protection Threshold MEM_REG
Internal Overtemperature
Hysteresis MEM_REG
Charging Current Reduction
Threshold
Charging Current Reduction Rate
SYMBOL
V
THM
R
THM
V
HOT
V
HYS-HOT
V
COLD
V
HYS-COLD
V
DISABLE
T
PROTECT_CCCV
CONDITIONS
(Notes 1, 12)
THM to C
BIAS
(Note 12)
(Notes 12, 13)
(Notes 12, 13)
(Notes 12, 13)
(Notes 12, 13)
(Notes 12, 13)
(Note 12)
0.02
0.727
9.8
0.271
MIN
TYP
V
CBIAS
10.0
0.283
0.3055
0.739
0.714
0.03
160
-20
165
-15
100
133
0.04
0.748
10.2
0.292
MAX
UNITS
V
k
Ratio to
V
CBIAS
Ratio to
V
CBIAS
Ratio to
V
CBIAS
Ratio to
V
CBIAS
Ratio to
V
CBIAS
°C
°C
°C
°C
°C
mA/°C
DS2731
T
HYS-PROTECT_CCCV
(Note 12)
T
PROTECT_MEMREG
T
HYS-PROTECT_
MEMREG
(Note 14)
(Note 14)
(Note 12)
(Note 12)
T
CHOKE
T
CHOKE_RATE
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
Note 10:
Note 11:
Note 12:
Note 13:
Note 14:
All voltages referenced to AGND pin.
V
CIN
is equivalent to V
AUX
when V
AUX
is greater than V
TRIP
, otherwise V
CIN
is equivalent to V
BATT+
.
Supply-current specification is only for current drain of the IC and does not include cell-charge current, load-supply cur-
rent, or any external resistor bias currents. The only exception is I
SLEEP
, which does account for complete current drain of
the lithium cell during low-battery conditions.
Below this voltage, the input is guaranteed to be logic-low.
Operating from 3.3V ±10%.
Above this voltage, the input is guaranteed to be logic-high.
Assumes an R
SNS
value of 0.05Ω.
Relative to V
CV
.
With recommended application circuit.
Includes complete package resistance.
This specification is from the rising or falling edge of
ENS
to the closure of the switch and includes whatever delay is in the
internal logic and FET drivers.
Applies to charger.
Multiply these values by C
BIAS
voltage to get value in volts. Recommended value of resistor in divider network is 10kΩ ±1%.
Tolerance includes tolerances of internal resistance and C
BIAS
voltage.
Applies to memory buck regulator.
_______________________________________________________________________________________
5
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